Collapse mechanisms of out-of-plane preload composite sandwich beams under in-plane loading

Abstract

This study extends the knowledge of the characteristics of composite sandwich beams under combined out-of-plane and in-plane loadings. Angle-ply GFRP composite laminate skins with different densities PVC foam cores, have been manufactured by VARTM process to fabricate sandwich panels. The fabricated panels were statically tested in flexure and tension to obtain the combined mechanical properties and determine the collapse mechanisms. This study is important in applications where the flexural stress is low and axial stress is relatively high. It investigates the properties for panels preloaded in flexure and tested under in-plane tensile. The effect on stiffness, strength, and collapse mechanism with changes in foam core density is investigated. To investigate the microscopic mechanisms and the microstructural changes of the preloaded beams, SEM and Optical Microscopy were both used. DIC was also used to map out the deformation growth during the tensile loading. A two-parameter Weibull distribution function is used for systematically analyzing the probability of GFRP sandwich beams with H80, H100 and H200 foam cores under tensile stress. The numerical finite element analysis have been performed to predict, compare with the experimental results and to capture the corresponding collapse mechanisms. Excellent agreement is found between the experimental and the proposed model in terms of damage shape and ultimate failure load. Depending upon the choice of foam core density and percentage of preloading level, prefailure collapse mechanism (before tensile test) is by skin microbuckling, indentation and wrinkling beneath the central roller during three-point bending test. These local failure modes are directly affected the in-plane tensile mechanical properties of the composite sandwich beams. Denser foam core contributes well on the in-plane mechanical stability of the composite sandwich beams.